What to Know Before Starting Intermittent Fasting: 5 Scientific Considerations

Intermittent fasting, or IF, has gained a lot of traction for the potential health benefits of the diet. Some IF-ers report more energy, weight loss, and improved metabolic health. (1) But intermittent fasting is not for everyone. There are a few health considerations you may want to think about before you get started.

Some research suggests that people with certain health conditions, such as those that affect digestion or blood sugar or those in life stages, should be careful before starting transitional fasting. (4) Let’s break down the research-backed considerations to help you decide if intermittent fasting is right for you and your lifestyle.

Medical Conditions and Medications: Who Should Avoid Intermittent Fasting?

Before jumping on the intermittent fasting bandwagon, you should consider your personal medical history and current medications and as always, talk to your doctor. In particular, those with diabetes, kidney stones, or gastroesophageal reflux disease should approach fasting with caution and seek specific advice before starting to fast. (4) (5)

Additionally, if you take medications for heart disease, blood sugar, high blood pressure, or medications that require food for proper absorption, intermittent fasting may affect their effectiveness or have side effects. (6) Anyone with a history of eating disorders should avoid intermittent fasting, because any type of diet plan can trigger unhealthy patterns of food restriction and overeating. (7)

Medical Conditions That Can Make Intermittent Fasting A Bad Idea

If you are taking medication for any medical condition, including heart disease, diabetes, high blood pressure, or medications such as insulin and blood thinners may require frequent meals for proper absorption, intermittent fasting is recommended. It may not be right for you. (6)

Here are some other health conditions that may rub intermittent fasting the wrong way:

• DiabetesFasting affects blood sugar levels, causing dangerous drops or unpredictable spikes. (4)
• Kidney Stones: Fasting can increase the risk of stone formation by affecting hydration levels and food intake.(5)
• Underweight IndividualsFasting can lead to excess weight, so it should be done under medical supervision and regular health care checks. (8)
• History of Eating Disorders: Fasting can lead to unhealthy eating habits, making it unsafe for those with past or current eating disorders. (7)

Effects of Intermittent Fasting on Metabolism

One of the most talked about benefits of intermittent fasting is its effect on metabolism. Research suggests that fasting kick-starts fat burning through a process called ketosis. That’s when the body burns fat for energy in the absence of carbohydrates. (1)

In addition, intermittent fasting can improve insulin sensitivity, potentially reducing the risk of developing type 2 diabetes by lowering blood sugar levels and promoting better glucose control. (9)

However, notable studies indicate that when compared head-to-head with other types of controlled diets, fasting is not associated with significantly greater weight loss than other types of calorie-restricted diet plans. (10)

This means that if you are not a good candidate for fasting, any type of diet that works for you can still work to help you achieve your weight loss goals.

Another metabolic benefit is autophagy, a process of cellular repair and regeneration that occurs in any form of calorie restriction. (11) This process has been linked to longevity and may protect against age-related diseases by clearing damaged cells. (11)

Hormonal Effects: Why Fasting May Be Different for Women

Women’s bodies are more sensitive to changes in calorie intake, which is why intermittent fasting can affect female hormones such as estrogen and progesterone. (12)

Studies show that excessive fasting may disrupt the balance of reproductive hormones in women, potentially leading to irregular menstrual cycles and unpleasant symptoms. (12) Importantly, women trying to conceive may want to avoid long fasting windows, as calorie restriction can negatively affect fertility. (12)

For women who are pregnant or breastfeeding, fasting can lead to malnutrition and low calorie intake, which can affect the health of both mother and baby. (13) If you are a woman at this stage of life, consult your health care team before attempting fasting.

Even outside of pregnancy, women with hormonal imbalances such as polycystic ovary syndrome (PCOS) should be careful with fasting. It can make symptoms worse. (13)

Finally, some studies suggest that women may benefit from shorter fasting windows, such as 12 to 14 hours instead of a limited schedule of 16 hours. (14)

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About the Experts:

Caroline Thomason is a delicious nutritionist and educator who combines her love of nutrition with the ability to make better health easy to understand. With 12 years in the industry, she has published in over 40 publications, is a consultant and CPG consultant, speaker, broadcaster, and food developer.

Joanna Gregg, RD is the creator of the MyFitnessPal food database. She received her bachelor’s degree in Nutrition from Georgia State University and her master’s degree from the University of Nebraska.

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Cortisol and Stress: The Science of Fasting and the Stress Response

Intermittent fasting can also affect your cortisol levels, the hormone responsible for managing your body’s stress response. (15)

Prolonged fasting can increase cortisol production, especially if you’re already stressed or sleep-deprived. (15) Elevated cortisol levels appear to be associated with weight gain, particularly in the abdominal area, which may counteract the weight loss benefits associated with fasting. (16)

Even worse, high cortisol levels may cause you to eat food when the fasting window ends, creating a cycle of eating followed by intermittent fasting. (17) This is a type of eating disorder, if you find yourself falling into this pattern, it may not be suitable for fasting. (17)

In general, if you are prone to stress or have difficulty managing stress-related cravings, intermittent fasting may not be the best option.

Blood Sugar Sensitivity: Who Should Be Careful?

If you have blood sugar concerns, such as diabetes or hypoglycemia, you need to be especially careful with intermittent fasting. (4) While fasting may improve your insulin sensitivity, it can be dangerous for those with diabetes, because prolonged fasting can lead to low blood sugar levels. (9)

Especially if you take insulin or other medications that affect blood glucose, fasting can increase the risk of hypoglycemia, which can cause serious symptoms such as dizziness, brain fog, confusion, or fainting. (18)

Even in those without diabetes, long periods of fasting can cause low blood sugar, leading to irritability or a general feeling of fatigue. (19) If you have a blood sugar-related condition, consider shorter fasting windows or talk to a health care professional to find the safest method.

Topic: Is Intermittent Fasting Right For You?

While intermittent fasting has become popular for its potential benefits for metabolic health, it’s not right for everyone. Before you dive in, consider how fasting can affect your hormones, metabolism, stress levels, and blood sugar regulation.

For any new diet, consult a health care provider such as a dietitian or doctor. If fasting isn’t for you, there are endless options for your nutrition plan to help you reach your goals.

And if you decide to give it a try, be sure to check out the Intermittent Fasting Tracker in the MyFitnessPal app.

Frequently Asked Questions

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